1. Field of the Invention
This invention relates to a sputtering apparatus used for fabrication of various kinds of semiconductor devices, especially to an ionization sputtering apparatus which has a function for ionizing sputtered particles.
2. Description of Prior Art
In fabrication of semiconductor devices, sputtering process is widely utilized for depositions of many kinds of films such as wiring metal films and barrier films preventing cross-diffusion of dissimilar layers. In various properties of sputtering apparatuses, high step coverage onto a hole formed on a substrate has been more significant recently.
Specifically, in the structure of CMOS-FET (complementary metal-oxide-semiconductor field effect transistor), which is broadly used in DRAM (dynamic random access memory), a barrier film is deposited onto a contact hole formed above a channel so that the cross-contamination of contact metal and the channel material. In multi-layer wiring structures, a via hole is formed through an inter-layer insulation film and is filled with inter-layer wiring metal. A barrier film is also formed on the surface of the via hole for prevention of cross-contamination. Aspect ratio, which means ratio of hole depth against hole width, of these holes has been higher and higher by years on the ground that integration scales of devices have been increased. For example, the aspect ratio rises up to about 5 or 6 in 256 Mbit class DRAM, though it is about 4 in 64 Mbit class DRAM.
In deposition of the barrier film onto a hole such as a contact hole or via hole, amount of deposition on the bottom surface of the hole needs to be to 10 to 15% of that on the surface outside the hole. It is, however, difficult to deposit a film onto a hole having a high aspect ratio at high bottom coverage. Bottom coverage means proportion of a deposition rate onto the bottom of a hole against that onto the outside of holes. When the bottom coverage is decreased in the barrier film deposition, crucial defects such as the junction leak which affect device properties might occur, because the barrier film is thinner at the bottom.
As a method for improving the bottom coverage, such a method as collimate sputtering and low-pressure long-distance (LPLD) sputtering have been developed. The collimate sputtering is the method to make sputtered particles flying vertically to a substrate arrive at the substrate selectively, by providing between the target and the substrate a board called xe2x80x9ccollimatorxe2x80x9d having many through holes elongated vertically to the substrate. The LPLD sputtering is the method to make sputtered particles flying vertically to a substrate arrive at the substrate selectively, by enlarging the distance from the target to the substrate up to about the 3 to 5 times of that in usual sputtering, and reducing the pressure, for example below 0.8 mTorr, to enlarge the mean free path so that those sputtered particles may not collide with each other to scatter away.
The collimate sputtering, however, has a problem that the sputter rate is decreased because sputtered particles are wastefully deposited on the collimator. The LPLD sputtering also has the problem of the sputter rate decreasing. For the LPLD sputtering, it is essential because the pressure is reduced and the target-substrate distance is enlarged. Because of these problems, it is a fact that the collimate sputtering can not be used for processes further than the mass production of devices up to 16 Mbit class having holes of aspect ratios up to about 3. The LPLD sputtering is supposed to have the limitation at the aspect ratio about 4 as well.
Considering the situation described above, this invention is given an object to enable a high step coverage thin-film deposition onto a hole with an aspect ratio over 4.
To achieve this object, this invention presents an ionization sputtering apparatus, wherein an ionization means generates a plasma at an ionization space between a target and a holder holding a substrate, and a magnetic device preventing the plasma from diffusing from the ionization space is provided.
To achieve this object as well, this invention presents an ionization sputtering apparatus, wherein an ionization means generates a plasma at an ionization space between a target and a holder holding a substrate, and a magnetic device orienting ionized sputtered particles toward the substrate is provided.